Elimination of contact burning on controls



June 9, 1942. E Q TANNER 2,285,624

BLIIIRATION 0F CONTACT BURNING Oll CONTROLS Filed Nov. 4, 1939 'lll/(IIIA XII wmmssss: I mamon Elo L. Tanner.

Patented June 9, 1.942

ELIMINATION F CONTACT BURNING 0N CONTROLS Elo '0. Tanner, Sprlngeld, Mass., assignor to Westinghouse Electric Manufacturing Company, East Pittsbur Pennsylvania gh,- Pa., a corporation of lApplication November 4, 1939, Serial No. 302,894

' (cieco- 166) 2 Claims.

My invention relates to an electrical switch and more specifically to an electrical switch which will be devoid of arcing or sparking across its contacts.

In electrical switches of well known design, there is sometimes a failure to either snap open or close firmly. As a result of this, sparking or arcing occurs and in time this arcing or sparking burns the contacts and may even start a iire.

An object oi my invention is to provide an electrical switch in which at least one of its contact elements incorporates the use of a bimetal, thereby minimizing or eliminating the possibility of the occurrence of sparking across the contact members. A

Another object of 'my invention is to provide an electrical switch which is self adjusting withA respect to imperfections which arise during manufacture which cause uneven bearing of the movable contact member with respect to the stationary contact member.

Other objects and advantages will become more apparent from a study of the following specification when considered in conjunction with the accompanying drawing, in which:

Figure 1 is a diagrammatic showingY of a switch involving the principles o f my invention; l

Fig. 2 shows the same switch illustrated in Fig. 1 except that. the parts assume a different position as the result of arcing across the contact members; and

Fig. 3 shows a switch which, due to defective manufacture, has uneven bearing or contact pressure between the movable and stationary contact members. f

" .Referring more particularly to Figures 1 and 2, numerals 'l and 2 denote theI stationary support members which carry the stationary contact elements l and 4, respectively. -A movable contact element comprises a `contact-.carrying arm i having rigidly secured thereto a stem 0 with an enlargement at the .flower extremity thereof -and a spring 1 which normally urges the movable contact element l of silver or ythe like into intimate engagement Vwith the stationary contact elements I and 4." The movable contact element lin accordance with my invention has a bimetallic backing element I.

Assume that the switch'is in the closed position. as shown in.Flg. 1l and that no sparking occurs across the contacts. Thus, the elements I and )assume a substantially nat position, such as shown in Fig'. 1. Spring 1 in this instance, will bias the contact element l into engagement with the stationary contact members.

Assume now that due to poor contact pressure or the like, sparking or arcing occurs between the movable and stationary contact members resulting in heating of movable contact element 3 and its bimetallic backing element 9. The effect ol this heat will be to cause a distortion or curvature oi the bimetallic element together with the movable contact element 8 rigidly secured thereto, such as shown (exaggerated) in Fig. 2. This distorted shape of elements I ands which is shown exaggerated for purposes of explanation will accomplish two things; one,

if the switch is closed and not ready to open yet, the curvature increases the contact pressure by compressing spring 1 resulting in reduction of heat generated, and two, if the switch is on the verge of being opened, the additional force `or motion resulting from the curvature will aord snap action in the separation of the contact members and in the case of a toggle switch (not shown) will snap such switch overcenter and open the circuit.

It will be obvious that the same benefits will be obtained if the stationary contactvmembers may incorporate the bimetal instead of the movable contact members or if the switch comprised only a pair of contact members, one movable and one stationary, one of which contact members included the bimetal. It will be apparent further that element 8 itself may be parto! a bimetallic element with element l as the other part instead of element Q being the complete bimetallic element.

Another advantage of the switch in accordance with my invention is'that it tends to correct itself vi'or imperfections or variations in manufacture which cause uneven contact pressure between the movable and the two stationary contact members. as shown in Fig. 3, wherein, at the right-hand side a small separation or gap (shown enlarged) occurs causing arcing between the right-hand stationary contact memberand the contiguous movable contact portion. 'As the result of this arcing, the movable contact element will flex, as shown in dotted establishing contact relationship between the movable contact member and both of the stationary contact members. It will thus be lseen that the manufacturing defectskresulting in imperfect contact will automatically correct Athemselves. v

Another advantage is the inherent wiping acvcon soi-ded by the curving or the bimetal which helps 'to clear the surfaces. Furthermore,

successful operationof my device can be obtained lines. thereby re,`

even without arcing, in other words, poor contact pressure may cause high resistance and consequent heating without the occurrence of arcing.

I am, of course, aware that others, particularly after having had the benefit of the teachings of my invention, may devise other devices embodying my invention, and I, therefore, do not wish to be limited to the specic showings made in the drawing and the descriptive disclosure hereinbefore made, but wish to be limited only by the scope of the appended claims and such prior art that may be pertinent.

I claim as my invention:

1. An electrical switch including a pair of cov acting contact members, one of said contact members comprising a centrally supported member with freely movable extremities which member serves as the current bridging member having superposed thereon a second metallic piece .having a different coefficient of expansion than the first thereby forming therewith a bimetallic element, the other of said contact members consisting of two flat separate metallic pieces 1ocated in thei same plane and which are parallel to the first mentioned bimetallic contact member, and helical spring means for centrally supporting said centrally supported contact member and acting to'normally bias said contact members s stationary contact members, a spring which centrally supports said movable contact member for normally urging the extremities of said bimetallic contact member into engagement with said stationary contact members when in the closed position and adapted to progressively increase said contact pressure as the 'result of deformation of the bimetallic contact member and comi pression of said spring which occurs as the result of temperature rise such as due to arcing.

ELO C. TANNER. 

